Frequently, in industrial waste treatment, waste water treatment or in brewing plants or the like, an accurate measurement of the organic content of a fluid may be required so as to determine, for example, the treatment or filtration efficiency of the plant. Typically, any such measurements are taken only once during the working day, which is insufficient to identify fluctuating organic loads within the fluid, thus leading to inefficient treatment of the fluid due because of use of non-optimal conditions for treatment of the fluid.
Furthermore, waste water of both domestic and industrial origin is frequently treated by a biological aerobic process which uses suspended micro-organisms (the activated sludge process). The biomass concentration is an important parameter in maintaining effluent quality. It is generally measured off-line as dry weight. On-line probes based on, for example, turbidity, are generally unreliable and measure inert particles and dead cells.